HiRISE clocks hurricane-speed winds on Mars

Orbiting camera measures swirling gusts in dust devils

Among other things, dust devils carving
trails through the planet’s reddish sands kick junk into its
atmosphere. But though scientists have been able to estimate how
quickly these devils travel across the rocky landscape, no one could really
pinpoint the speed of the the swirling winds inside them until
recently. Previous measurements of the extraterrestrial whirling
dervishes’ interiors were rare, and fraught with complicated
assumptions.

The devil is in the details, indeed.

Then along came David Choi, a postdoc
at NASA’s Goddard Space Flight Center in Greenbelt, Md.

Choi decided to track dust devil wind speeds using data from HiRISE,
a camera on the Mars Reconnaissance Orbiter that snaps high-resolution photos of the planet’s surface. Sometimes, HiRISE captures a dust devil in action, creating a somewhat
time-lapsed view of the devil’s progress. Using these lucky frames,
Choi could track distinct cloud features within four individual
devils and, knowing how much time had elapsed between photos,
determine how fast the swirling clouds were moving.

The answer was somewhat surprising: In
some cases, wind speeds within the columns whipped around at 45
meters each second — what we Earthlings would consider “hurricane-force,” or above 33
meters per second. Other times, the weather inside these alien
tornadoes was milder, though typical wind speeds varied between 20
and 30 meters per second. He presented these results October 3 in Nantes, France, at the joint meeting of the European Planetary Science Congress and
the American Astronomical Society’s Division for Planetary Sciences.

“As a whole, they’re not like a
hurricane, but there are pockets or gusts that exceed
hurricane-force,” Choi says.

Some other funnies: All the devils were
observed at roughly 3p.m. MLT. That’s Mars Local Time. They ranged
from 30 meters to 250 meters in diameter, and towered between 150
meters and 700 meters into the Martian sky.